1. Field of the Invention
The present invention relates to an internal combustion engine intended to reduce the emission of the harmful components of engine exhaust gas and prevent increase in the fuel consumption normally caused by an emission control. Particularly, the invention is concerned with an internal combustion engine equipped with a system for converting a mixture of air and methanol into a reformed gaseous mixture rich with hydrogen and for supplying the reformed gaseous mixture to the engine to thereby improve the combustion therein.
2. Description of the Prior Art
In order to reduce the emission of harmful components of engine exhaust gases, there has been proposed an internal combustion engine of an arrangement such that, before a hydrocarbon fuel such as gasoline is mixed with air and introduced into a combustion chamber of the engine, the fuel is mixed with water, air and engine exhaust gas to form a mixture. The mixture is then fed into a reactor having catalysts which cause reaction between the components of the mixture at a temperature ranging from 250.degree. to 1,000.degree. C. so that a part of the fuel is converted into a reformed gaseous mixture including hydrogen or carbon monoxide. The reformed mixture is then introduced into a combustion chamber of the engine. There has also been proposed an another arrangement such that gaseous hydrogen from a hydrogen container is mixed with a hydrocarbon fuel and supplied therewith into a combustion chamber of an internal combustion engine.
The first arrangement required a water container which caused a problem such that the water in the container was frozen resulting in bursting of the container in winter season or a cold district. In the case where the fuel used contained a compound of lead, the engine exhaust gas which recirculated into the reactor contained the compound of lead by which the catalysts were damaged. Even in the case where the fuel did not contain a compound of lead, soot and/or tar was included in the engine exhaust gas and deposited on the surfaces of the catalysts to reduce the efficiency of the catalysts. The reformed gaseous mixture, moreover, included gaseous components which were unnecessary for the engine operation and which reduced the efficiency of charge of the reformed gaseous mixture into the combustion chambers of the engine and adversely affected the engine performance. Furthermore, when a fuel containing cyclic hydrocarbon and gum, such as gasoline, light oil or kerosene, soot or tar was deposited on the surfaces of the catalysts, the inner surface of the reactor and the passages extending between the reactor and the combustion chamber of the engine, deterioration of the catalysts and blockade of the passages resulted.
The second arrangement required a hydrogen bottle which presented a danger of explosion. The hydrogen bottle was inevitably bulky in size and heavy. Thus, the second arrangement was not suitable for an internal combustion engine for use in an automobile.
So as to purify engine exhaust gases, there has also been proposed a torch ignition type (or stratified charge) internal combustion engine comprising a main combustion chamber for receiving a lean air-fuel mixture and an auxiliary chamber (to be called "trap chamber" hereinunder) for receiving a rich mixture to be ignited by a spark plug to form a flame by which the lean mixture in the main chamber is ignited to produce power therein. The total of the lean and rich mixture is lean as a whole to reduce the harmful components of the engine exhaust gas. With this type of the engine, it has been found that the engine is operable by the ignition of an air-fuel mixture having an air-fuel ratio up to about 18 to 24 contrary to the upper limit air-fuel ratio of about 18 for the operation of a normal internal combustion engine without a trap chamber. It has been known that, in order to effectively attain the reduction in the emission of harmful nitrogen oxides (NO.sub.x) contained in engine exhaust gases, an air-fuel mixture must be burnt at a very lean air-fuel ratio of larger than 18. The problem caused when such a very lean air-fuel mixture is burnt in the torch ignition type combustion engine is that variation of cycle timing due to delayed ignition of the lean mixture or delayed propagation of flame causes variation of torque on the output shaft of the engine with a resultant tendency that, when the engine is mounted in an automobile, a surging is caused by the engine torque variations and a resonance of the engine with the power trains results. This greatly lowers the operability of the automobile notwithstanding the fact that combustion of the lean air-fuel mixture is possible with the engine. In addition, with an air-fuel mixture having an air-fuel ratio of larger than 20, the volume of the non-combustible strata of the mixture adjacent to the walls of the combustion chamber is increased with a disadvantageous problem that the emission of unburnt hydrocarbon (HC) is extremely increased.